Active Noise Cancellation, or ANC, (RPO VQN) is being introduced on 2010 Equinox and Terrain models equipped with the 2.4L SIDI 4-cylinder engine (RPO LAF). It works to reduce noticeable noise at certain vehicle speeds by creating sound waves at a precise frequency, resulting in improved quietness with less mass -- and better fuel economy -- than using additional sound-deadening insulation.
The ANC system has four main components:
· ANC module
· Microphones (2)
· Audio amplifier
· Speakers
ANC uses an RPM signal from the tachometer to determine the rotational speed in the engine along with in-vehicle microphones to monitor low-frequency engine drone. The microphones are connected to the audio system and pick up the sound/noise in the vehicle's cabin while the speakers produce the cancellation vibrations.
The two microphones are centrally located in the headliner to detect noise in the vehicle caused by the engine. The processor analyzes the noise signal and outputs a cancellation signal audio tone based on positive coefficient and phase change to moderate the engine noise and make the vehicle seem quieter. The ANC module then sends an "anti-noise "amplified signal to the speaker and subwoofer, which is mixed within the audio amplifier with the regular audio (CD/radio, etc).
TIP: ANC does NOT cancel wind noise, road noise, or any engine noise above 2000 RPM.
TIP: For optimal ANC performance, do not block the cargo area speaker. (Fig. 2)
Commonly Misidentified Issues
· ANC is not working
If a customer knows the vehicle has ANC, it may be a common misperception that ANC is not working because the engine still makes noise. The ANC module only cancels particular frequencies of noise caused by transmission lockup. It is meant to bring the engine noise back to an acceptable level, not create a noise-free environment, such as noise-cancelling headphones.
· The subwoofer is not working
Vehicles equipped with the base-level audio system (RPO UW6) and ANC (RPO VQN) will have a subwoofer in the rear compartment. The subwoofer is necessary for ANC operation and is used only for ANC on vehicles equipped with the base-level audio system. With UW6, no CD or radio audio output will come out of the subwoofer (strictly dedicated for ANC).
Diagnostics/Service
The ANC module has an internal microphone-check diagnostic mode. This can be used to check microphone connectivity. Please see the Service Information for diagnostic tone testing (Document ID# 2274156)
ANC Limiter Shutdown
The ANC module (Fig. 3) has a self-protect mode where it will shut down if the cabin environment changes in a way where noise can no longer be canceled (i.e., odd combination of open windows, etc).
An output limiter is part of the ANC programming, so it may shut down during an ignition cycle to prevent ANC overload. ANC will resume normal operation on the next ignition cycle. If this shutdown happens while a customer is driving, more engine noise than normal may be noticeable.
ANC Labor Code
The labor code associated with ANC repair/replace is R0150.
TIP: Keep in mind that ANC is part of the audio system and that the amplifier, radio, speakers and microphones all need to be working for ANC to function properly. For example, intermittent microphone connectivity will lead to unstable ANC operation.
- Thanks to Matthew Berg, David R. Baer, and Katul Patel